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Implicit Modeling of the Impact of Adsorption on Solid Surfaces For Implicit Modeling of the Impact of Adsorption on Solid Surfaces for Protein Mechanics and Activity with a Coarse-Grain Representation Nicolas Bourassin, Marc Baaden, Elisabeth Lojou, Sophie Sacquin-Mora To cite this version: Nicolas Bourassin, Marc Baaden, Elisabeth Lojou, Sophie Sacquin-Mora. Implicit Modeling of the Impact of Adsorption on Solid Surfaces for Protein Mechanics and Activity with a Coarse- Grain Representation. Journal of Physical Chemistry B, American Chemical Society, 2020, 15, 10.1021/acs.jpcb.0c05347. hal-02939019 HAL Id: hal-02939019 https://hal.archives-ouvertes.fr/hal-02939019 Submitted on 18 Sep 2020 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Implicit modeling of the impact of adsorption on solid surfaces for protein mechanics and activity with a coarse-grain representation Nicolas Bourassin1,2, Marc Baaden1,2, Elisabeth Lojou3 and Sophie Sacquin-Mora1,2* 1CNRS, Université de Paris, UPR 9080, Laboratoire de Biochimie Théorique, 13 rue Pierre et Marie Curie, 75005 Paris, France 2Institut de Biologie Physico-Chimique-Fondation Edmond de Rotschild, PSL Research University, Paris, France 3Aix Marseille Univ, CNRS, Bioénergétique et Ingénierie des Protéines, UMR 7281, 31, chemin Joseph Aiguier, CS 70071 13402 Marseille cedex 09, France *Corresponding author e-mail: [email protected] Running title : A coarse-grain model for proteins on solid surfaces Keywords: Protein mechanics, protein adsorption, coarse-grain simulations, elastic network model A preliminary version of this work, was deposited in bioRxiv. doi: https://doi.org/10.1101/2020.03.30.015537 1 Abstract Surface immobilized enzymes play a key role in numerous biotechnological applications such as biosensors, biofuel cells or biocatalytic synthesis. As a consequence, the impact of adsorption on the enzyme structure, dynamics and function needs to be understood on the molecular level as it is critical for the improvement of these technologies. With this perspective in mind, we used a theoretical approach for investigating local protein flexibility on the residue scale that couples a simplified protein representation with an elastic network and Brownian Dynamics simulations. The impact of protein adsorption on a solid surface is implicitly modeled via additional external constraints between the residues in contact with the surface. We first performed calculations on a redox enzyme, bilirubin oxidase (BOD) from M. verrucaria, to study the impact of adsorption on its mechanical properties. The resulting rigidity profiles show that, in agreement with the available experimental data, the mechanical variations observed in the adsorbed BOD will depend on its orientation and its anchor residues (i.e. residues that are in contact with the functionalized surface). Additional calculations on ribonuclease A and nitroreductase shed light on how seemingly stable adsorbed enzymes can nonetheless display an important decrease in their catalytic activity resulting from a perturbation of their mechanics and internal dynamics. 2 1.Introduction The interaction of proteins with solid surfaces is of crucial importance in the field of biomaterials1, since it plays a key role in numerous applications, such as tissue engineering and regenerative medicine (where we need to know the cellular response to implanted materials), the optimization of surfaces for biosensors, the development of bioactive nanoparticles, biocatalysts or bioanalytical systems. One of the main issues that are addressed when investigating protein/surface interaction, is the matter of protein orientation. Controlled adsorption with ordered proteins is essential for devices such as biosensors, where antibodies should be immobilized with a specific orientation favoring the following antibody-antigen binding2, or for bioelectrocatalysis devices (biofuel cells or bioreactors for electrosynthesis), where a correct enzyme orientation is essential for direct electron transfer between the adsorbed protein and the electrode3-4. The adsorbed proteins’ orientation depends on many factors, such as their charge, size or shape, the support properties, or external conditions like the temperature and pH5-7. Hence these devices require a specific functionalization of the surface, in order to fine tune its charge and physico-chemical properties, that can be achieved with self assembled monolayers (SAMs) for example. For both cases, the conservation of the adsorbed proteins’ native conformation (and hence their biological function) is another key aspect that has to be taken into consideration. On the opposite end of the applications spectrum, the development of materials resisting protein adsorption has also drawn much attention, since it has practical uses, such as marine antifouling or antimicrobial coating for medical devices. In that case the challenge will be to design biomaterials where proteins will not adsorb8-10. 3 All these phenomena have now been under scrutiny for several decades, but reaching a detailed understanding of the molecular mechanisms associated with biomolecular adsorption on functionalized surfaces is far from being achieved. In particular, considerable experimental works have been conducted until now, such as atomic force microscopy, mass spectrometry and various spectroscopies11-12. However, the resolution of current experimental techniques is still insufficient to quantitatively determine the range of potential orientations and conformations of adsorbed proteins on the atomistic level. In that perspective, molecular simulations play an increasingly important role in revealing the mechanisms of chemical and biological processes taking place on the bio- nano interface, and designing new products. For over ten years, molecular simulation techniques have been developed to address these issues, using multiscale approaches combining all-atom and coarse-grain models13-15, and represent a promising tool for the biomaterials field16-18. Numerous studies focus on the prediction of the adsorbed protein orientation and binding modes on the surface, which have to be controlled for example to ensure that an enzyme’s catalytic site will remain accessible after adsorption; and on the impact of adsorption on protein structure, since conformational changes are indeed likely to perturb an enzyme’s catalytic activity19-22. However, proteins are known for being flexible objects, and their internal dynamics play a central role for their biological function23-24. As a consequence, one also has to consider how surface binding will affect an enzyme’s motions to determine whether it will remain functional in its adsorbed state. In that perspective, we used a coarse-grain, elastic network representation to implicitly model the impact of surface adsorption on protein mechanics. We first performed calculations on the redox enzyme bilirubin oxidase (BOD) from the fungus 4 Myrothecium verrucaria, to study the impact of adsorption on its mechanical properties. The resulting rigidity profiles show that, in agreement with the available experimental data, the mechanical variations observed in the adsorbed BOD will depend on its orientation and its anchor residues (that are in contact with the solid surface). Additional calculations on ribonuclease A and nitroreductase shed light on how seemingly stable adsorbed enzymes can nonetheless display an important decrease in their catalytic activity resulting from a perturbation of their mechanics. 2.Material and Methods Brownian Dynamics simulations Rigidity profile of a protein Coarse-grained Brownian Dynamics (BD) simulations were run using a modified version of the ProPHet (Probing Protein Heterogeneity, available online at https://bioserv.rpbs.univ-paris-diderot.fr/services/ProPHet/) program25-27, where additional external mechanical constraints can be applied between a set of residues defined by the user. In this approach, the protein is represented using an elastic network model (ENM)28-29. Unlike most common coarse-grained models where each residue is described by a single pseudoatom30, ProPHet uses a more detailed representation31 that involves up to 3 pseudoatoms per residue and enables different amino acids to be distinguished. Pseudoatoms closer than the cutoff parameter Rc = 9 Å are joined by Gaussian springs which all have identical spring constants of γstruct = 0.42 N.m-1 (0.6 kcal.mol-1.Å-2). The springs are taken to be relaxed for the experimentally observed conformation of the protein. Note that the ENM used in this work is a two- parameters model, comprising the cutoff distance and the spring constant, which does not explicitly model electrostatic interactions. However, the elastic network is built 5 from the protein folded crystallographic structure, and therefore takes into account, in an implicit manner, all the interactions (electrostatic, or hydrogen bonds) which contribute to shape the protein in its final fold. Despite their apparent simplicity, ENMs have turned out over the years to be a remarkably efficient tool for linking a protein structure to its mechanic and
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